1. Field of the Invention
The present invention generally relates to a sheet stacker to stack an incoming sheet-type recording medium (hereinafter, “sheet”), and to an image forming apparatus, such as a copying machine, a printer, a facsimile, and a digital multifunction product, that includes the sheet stacker.
2. Description of the Related Art
A sheet stack position, to which a sheet is delivered and at which the sheet is stacked, is set differently depending on a use and/or the configuration of an image forming apparatus or an image forming system. Under such a circumstance, techniques aiming at providing a sheet stacker to stack output sheets in a limited space while ensuring a certain stack capacity have been disclosed. Known examples of the techniques include a technique disclosed in Japanese Patent Application No. 2008-110834, according to which a sheet stack position is located both above and below an image forming apparatus. According to the technique disclosed in Japanese Patent Application No. 2008-110834, the image forming apparatus includes an image forming unit that forms an image on a recording medium sheet, and an output unit that outputs the recording medium sheet to an internal sheet-output unit that includes a sheet output tray. The sheet output tray includes a loading surface, on which the recording medium sheet output from the output unit is to be stacked, and an angle-adjusting unit capable of changing an angle of the loading surface of the sheet output tray on a side close to the output unit relative to an output direction, in which the recording medium sheet is output from the output unit.
Examples of techniques for configuring an entire tray to be ascendible and descendible by using a motor are disclosed in Japanese Patent No. 4072515, Japanese Patent Application No. 2007-055722, Japanese Patent Application No. 2003-073009, and Japanese Patent Application No. 2006-240761. According to a technique disclosed in Japanese Patent No. 4072515 among these examples, an image forming apparatus includes an image forming unit that forms an image according to image data on a recording sheet being conveyed, a reading device that is arranged above the image forming unit and scans an original to obtain image data, a sheet stacker unit that is arranged in a space between the image forming unit and the reading device and that stacks an output sheet thereon, a sheet output unit that is arranged in a lateral direction of the space and that outputs a sheet to a sheet stacker unit. The image forming apparatus includes a drive unit that includes a motor that causes the stacker unit to ascend and descend. A sheet loading surface of the stacker unit is tilted such that a downstream portion of a batch transport unit in a transport direction is positioned higher, and the motor is arranged at a position that is below the sheet loading surface of the stacker unit and downstream relative to the batch transport unit.
Techniques for configuring an entire sheet output tray to be ascendible and descendible are disclosed in Japanese Patent Application No. 2007-055722, Japanese Patent Application No. 2003-073009, and Japanese Patent Application No. 2006-240761 as well.
Each of these techniques aims at increasing efficiency in loading output sheets by effectively utilizing a limited space; however, the technique disclosed in Japanese Patent Application No. 2008-110834 is disadvantageous in that because a fixed side of the sheet output tray extends substantially horizontally, if a highly-resilient sheet is placed on the sheet output tray, even when an angle of the loading surface of the sheet output tray is changed, the sheet can fail to follow the loading surface of which angle has been changed and block a sheet output port.
The techniques disclosed in Japanese Patent No. 4072515, Japanese Patent Application No. 2007-055722, Japanese Patent Application No. 2003-073009, and Japanese Patent Application No. 2006-240761 are also disadvantageous in requiring a large space below the image forming apparatus to allow the entire tray to move and requiring a space to allow a sheet located out of the apparatus to be out of the way of the tray because a position of a leading end of the sheet in a sheet transport direction varies depending on the orientation of the tray. These impose difficulty in achieving compact configuration and space saving.